1. Field of the Invention
This invention relates to a process of producing a water-soluble carboxymethyl ether of wood molasses. More particularly, it relates to such a process wherein oligomeric lignocarbohydrate materials derived from soda or carbonate pulping processes, and steam treatments of wood chips, sawdusts and the like are reacted with sodium chloroacetate in the presence of an alkali metal hydroxide and an aqueous medium.
2. The Prior Art
Hemicelluloses as a group of carbohydrates constitute between 40 and 50% of the total carbohydrates in wood. Due to the morphological and chemical characteristics, wood hemicelluloses are easily solubilized with alkaline solutions or with water at an elevated temperature. Thus, large quantities of wood hemicelluloses are removed from wood chips by hydrolytic processes during soda pulping, sodium carbonate semi-chemical processes, and steam treatments of woody materials. The pulping processes also generate a substantial amount of water-soluble saccharinic acids through alkaline "peeling" and "stopping" reactions of which the mechanisms have been well elucidated in the literature. The alkaline peeling reaction involves enolization, hydrolysis of .beta.-alkoxycarbonyl bonds and further degradation of the products of hydrolysis to hydroxy carboxylic acids, e.g., isosaccharinic acid. Stopping reactions involve degradation and intramoleculr rearrangements of wood carbohydrates to alkali-stable acids, e.g., glucosaccharinic acid.
Carboxymethylation of carbohydrates is a well known reaction in the prior art. Carboxymethyl cellulose was first patented in German Patent No. 332,703 by Jansen in 1918. Quite recently, a series of patents have been issured to cover the production of carboxymethyl polygalatomannan gum useful as thickening agents, e.g., U.S. Pat. Nos. 3,679,658, 3,712,883, 3,740,388, and 3,740,389. The production of carboxymethyl hemiceluloses recovered from the liquor of cold soda pulping was disclosed in U.S. Pat. No. 3,560,480 which teaches the use of the material as additives in the paper industry. These patents discloses products, the characteristics of which are quite different from those of the subject invention.
Carboxymethylation of carbohydrates, in general, involves a two-step reaction that may be represented as follows: ##SPC1##
According to reactions [1] and [2], it is essential in the formation of carboxymethyl carbohydrates that adequate amounts of hydroxide and chloroacetate be present for the reactions. However, in the presence of excess hydroxide and water, chloroacetate is hydrolyzed to inactive glycolate which does not react with the ionized hydroxyl groups in the anhydroglucose units and other sugar units of wood carbohydrates. To avoid this difficulty, the excess alkali and water are pressed from the alkali cellulose which is then reacted with dry sodium salt of monochloroacetate. This is possible only in the production of carboxymethyl cellulose, as alkali cellulose forms sheets which may be pressed on a hydraulic ram. With viscous materials like galactomannan and other hemicelluloses which cannot be formed in sheets, organic solvents either alone or in a mixture with a small quantity of water are usually used as diluents to facilitate stirring of the reaction mixture and reduce the extent of hydrolysis of chloroacetate during carboxymethylation. The organic solvents which are particularly useful are methyl sulfoxide (U.S. Pat. No. 3,560,480), isopropyl alcohol and other monohydric alcohols of 2 to 4 carbon atoms (U.S. Pat. No. 3,740,388, U.S. Pat. No. 3,740,389).
Therefore, it is a general object of this invention to provide a water-soluble, carboxymethylated product from wood-based carbohydrates.
Another object of this invention is to provide a process for reacting wood molasses with sodium chloroacetate and an alkali metal hydroxide in an aqueous medium in the absence of a solvent. The system devoid of organic solvents is beneficial for two obvious reasons. First, the process reduces the cost of production by eliminating the use of organic solvents. Second, the process does not need the removal of solvents that is costly and sometimes hazardous.
Still another object of this invention is to provide water-soluble wood-derived products which are good detergent builders, calcium sequestrants, corrosion control agents, herbicide dispersants and de-rusting chemicals.
Other objects, features and advantages of this invention will be apparent from reading the following detailed description.